The disclosures herein relate generally to computer systems and more particularly to a shielding apparatus for reducing electromagnetic emissions from a computer system.
In order to meet electromagnetic emissions regulations required by agencies such as the Federal Communication Commission (FCC), it is common practice to place a compliant and conductive grounding member between an expansion device of a computer and the computer chassis. The grounding member provides a ground path between the chassis and the card to aid in containing electromagnetic emissions within the chassis.
U.S. Pat. No. 5,653,396 discloses a grounding system for an electrical connector assembly which provides an interconnection between a PC card and a main printed circuit board. A header connector is mounted on the main printed circuit board and receives the PC card. Mating terminals are provided on the header connector and a receptacle connector on the PC card for interconnection of the PC card to electrical circuit traces on the main printed circuit board. At least one header grounding contact is mounted on the header connector adjacent, but spaced from, the terminals and is coupled to a logic ground circuit on the main printed circuit board. A card grounding contact is mounted on the PC card near the front insertion end thereof for engaging the header grounding contact and connecting the logic ground circuit of the main printed circuit board to a logic ground circuit on the PC card to provide a low impedance ground return.
U.S. Pat. No. 5,563,450 discloses a peripheral card including a two-part metal cover mounting a printed wiring board on a U-shaped plastic frame. The wiring board is spaced from inside surfaces of the cover preferably by a pair spring clips mountable on side edges of the wiring board, each clip having an apertured intermediate bight portion overlying, and in scraped contact with, ground contact pads on the board. Barbed-end spring fingers extend integrally from the bight portion preferably toward the board side edge to which it is affixed and into scraped contact with respective ones of the metal cover parts as the metal cover parts are assembled together. The clips hold the board from movement in the cover and electrically ground any static electrical charges on the metal cover parts to the contact pads and to a ground socket in the frame. The clips electrically ground the metal cover parts to provide electromagnetic shielding of the electrical circuitry on the wiring board.
U.S. Pat. No. 4,780,570 discloses an electromagnetic interference (EMI) shield for situations which require heavy-duty wiping insertions, such as occurring when a relatively heavy electronic assembly is to be removably inserted in a cabinet. In accordance with the invention, inexpensive integral EMI strips of conductive spring material are riveted to opposite cabinet walls so as to be adjacent the wiping sides of the inserted electronic assembly. Each EMI strip contains integral longitudinally spaced projecting fingers formed to provide durable and highly reliable EMI shielding capable of withstanding many insertions and removals.
A common commercially-implemented grounding member for use with expansion devices in a computer includes a metal shield with a series of compliant spring members. The spring members extend from a surface of the grounding member. The grounding member is positioned between the expansion device and the chassis. The ground path is created by the compliant spring members engaging against the expansion device and the shielding member being engaged against, or being attached to, the chassis.
Grounding members of this type are known to have a number of undesirable characteristics. First, these types of grounding members are easily damaged as a result of one or more of the spring members getting caught in the expansion cards during either removal or insertion of the expansion cards into the chassis. The spring members unintentionally entangle with notches in the expansion device. This results in the spring members being distorted, broken or otherwise disabled. Second, to ensure sufficient grounding performance and reliability, it is common for the grounding member to include a plurality of spring members. This increases the likelihood of one or more of the spring members being damaged. The use of a plurality of spring members significantly increases the forces associated with deflecting the spring members. With sufficient force, the grounding member can be distorted. The distortion may result in the grounding member interfering with cables being connected to the expansion cards in configurations where a cable connector is connected to the expansion device through an access opening extending through the grounding member.
Therefore, what is needed is a robust EMI shielding apparatus for use with a removable expansion device in an electronic device to reduce the potential for electromagnetic emissions from a chassis of the electronic device.
Accordingly, in one embodiment, a reliable, damage resistant electromagnetic shielding apparatus uses elongated grounding members that extend in a direction generally parallel to the direction of insertion and extraction of a corresponding expansion device. To this end, an apparatus for mounting a system component in a chassis includes an electrically conductive chassis having a grounding frame mounted therein. The grounding frame has an access opening formed therein which is defined by opposed edges thereof. A contact member is attached adjacent to each edge whereby each access opening includes opposed contact members. Each contact member is resiliently deflectable.
A principal advantage of this embodiment is that discontinuities and obstructions along the edge portions of an expansion device do not engage and damage the contact members.